1,427 research outputs found
Gapless Hartree-Fock Resummation Scheme for the O(N) Model
A modified selfconsistent Hartree-Fock approximation to the lambda*phi^4
theory with spontaneously broken O(N) symmetry is proposed. It preserves all
the desirable features, like conservation laws and thermodynamic consistency,
of the selfconsistent Dyson scheme generated from a 2PI functional, also known
as the Phi-derivable scheme, while simultaneously respecting the
Nambu-Goldstone theorem in the chiral-symmetry broken phase. Various
approximate resummation schemes are discussed.Comment: 13 pages, 10 figures / Version accepted by Phys. Rev. D: the
introduction has been expanded by a few remarks in order to further clarify
the goal of the pape
Field theoretic description of the abelian and non-abelian Josephson effect
We formulate the Josephson effect in a field theoretic language which affords
a straightforward generalization to the non-abelian case. Our formalism
interprets Josephson tunneling as the excitation of pseudo-Goldstone bosons. We
demonstrate the formalism through the consideration of a single junction
separating two regions with a purely non-abelian order parameter and a sandwich
of three regions where the central region is in a distinct phase. Applications
to various non-abelian symmetry breaking systems in particle and condensed
matter physics are given.Comment: 10 pages no figure
Study of the ground-state energy of 40Ca with the CD-Bonn nucleon-nucleon potential
We have calculated the ground-state energy of the doubly-magic nucleus 40Ca
within the framework of the Goldstone expansion using the CD-Bonn
nucleon-nucleon potential. The short-range repulsion of this potential has been
renormalized by integrating out its high-momentum components so as to derive a
low-momentum potential V-low-k defined up to a cutoff momentum Lambda. A simple
criterion has been employed to establish a connection between this cutoff
momentum and the size of the two-nucleon model space in the harmonic oscillator
basis. This model-space truncation approach provides a reliable way to
renormalize the free nucleon-nucleon potential preserving its many-body
physics. The role of the 3p-3h and 4p-4h excitations in the description of the
ground state of 40Ca is discussed.Comment: 4 pages, 1 figure, 1 table, to be published in Physical Review
Neutrino scattering off pair-breaking and collective excitations in superfluid neutron matter and in color-flavor locked quark matter
We calculate the correlation functions needed to describe the linear response
of superfluid matter, and go on to calculate the differential cross section for
neutral-current neutrino scattering in superfluid neutron matter and in
color-flavor locked quark matter (CFL). We report the first calculation of
scattering rates that includes neutrino interactions with both pair-breaking
excitations and low-lying collective excitations (Goldstone modes). Our results
apply both above and below the critical temperature, allowing use in
simulations of neutrino transport in supernovae and neutron stars.Comment: 22 pages, 9 figure
Quark description of the Nambu-Goldstone bosons in the color-flavor locked phase
We investigate the color-singlet order parameters and the quark description
of the Nambu-Goldstone (NG) bosons in the color-flavor locked (CFL) phase. We
put emphasis on the NG boson (phason) called ``H'' associated with the
symmetry breaking. We qualitatively argue the nature of H as
the second sound in the hydrodynamic regime. We articulate, based on a diquark
picture, how the structural change of the condensates and the associated NG
bosons occurs continuously from hadronic to CFL quark matter if the
quark-hadron continuity is realized. We sharpen the qualitative difference
between the flavor octet pions and the singlet phason. We propose a conjecture
that superfluid H matter undergoes a crossover to a superconductor with
tightly-bound diquarks, and then a crossover to superconducting matter with
diquarks dissociated.Comment: 14 pages, 1 table, 1 figure and confusing statements are correcte
Light Scalar Mesons as Manifestation of Spontaneously Broken Chiral Symmetry
Attention is paid to the production mechanisms of light scalars that reveal
their nature. We reveal the chiral shielding of the \sigma(600) meson. We show
that the kaon loop mechanism of the \phi radiative decays, ratified by
experiment, points to the four-quark nature of light scalars. We show also that
the light scalars are produced in the two photon collisions via four-quark
transitions in contrast to the classic P wave tensor q\bar q mesons that are
produced via two-quark transitions . The history of
spontaneous breaking of symmetry in quantum physics is discussed in Appendix.Comment: Talk at The International Bogolyubov Conference "Problems of
Theoretical and Mathematical Physics" devoted to the 100th anniversary of
N.N.Bogolyubov's birth that was held from August 21 to August 22,2009 in
Moscow at the Russian Academy of Sciences (RAS) and from August 23 to August
27, 2009 in Dubna at the Joint Institute for Nuclear Research (JINR
The Continuum Limit and Integral Vacuum Charge
We investigate a commonly used formula which seems to give non-integral
vacuum charge in the continuum limit. We show that the limit is subtle and care
must be taken to get correct results.Comment: 5 pages. Submitted to JETP Letter
Nuclear Structure Calculations and Modern Nucleon-Nucleon Potentials
We study ground-state properties of the doubly magic nuclei 4He, 16O, and
40Ca employing the Goldstone expansion and using as input four different
high-quality nucleon-nucleon (NN) potentials. The short-range repulsion of
these potentials is renormalized by constructing a smooth low-momentum
potential V-low-k. This is used directly in a Hartree-Fock approach and
corrections up to third order in the Goldstone expansion are evaluated.
Comparison of the results shows that they are only slightly dependent on the
choice of the NN potential.Comment: 5 pages, submitted to Physical Review
Mesoscopic Electron and Phonon Transport through a Curved Wire
There is great interest in the development of novel nanomachines that use
charge, spin, or energy transport, to enable new sensors with unprecedented
measurement capabilities. Electrical and thermal transport in these mesoscopic
systems typically involves wave propagation through a nanoscale geometry such
as a quantum wire. In this paper we present a general theoretical technique to
describe wave propagation through a curved wire of uniform cross-section and
lying in a plane, but of otherwise arbitrary shape. The method consists of (i)
introducing a local orthogonal coordinate system, the arclength and two locally
perpendicular coordinate axes, dictated by the shape of the wire; (ii)
rewriting the wave equation of interest in this system; (iii) identifying an
effective scattering potential caused by the local curvature; and (iv), solving
the associated Lippmann-Schwinger equation for the scattering matrix. We carry
out this procedure in detail for the scalar Helmholtz equation with both
hard-wall and stress-free boundary conditions, appropriate for the mesoscopic
transport of electrons and (scalar) phonons. A novel aspect of the phonon case
is that the reflection probability always vanishes in the long-wavelength
limit, allowing a simple perturbative (Born approximation) treatment at low
energies. Our results show that, in contrast to charge transport, curvature
only barely suppresses thermal transport, even for sharply bent wires, at least
within the two-dimensional scalar phonon model considered. Applications to
experiments are also discussed.Comment: 9 pages, 11 figures, RevTe
Bound States and Threshold Resonances in Quantum Wires with Circular Bends
We study the solutions to the wave equation in a two-dimensional tube of unit
width comprised of two straight regions connected by a region of constant
curvature. We introduce a numerical method which permits high accuracy at high
curvature. We determine the bound state energies as well as the transmission
and reflection matrices, and and focus on the nature of
the resonances which occur in the vicinity of channel thresholds. We explore
the dependence of these solutions on the curvature of the tube and angle of the
bend and discuss several limiting cases where our numerical results confirm
analytic predictions.Comment: 24 pages, revtex file, one style file and 17 PostScript figures
include
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